This invention relates to cooling towers and to methods for optimizing the use of water and electricity in such towers. The invention relates more particularly to forced air cooling towers for an air conditioning system and a method for optimizing the use of water and electricity in such systems.
Air conditioning is a necessity for comfortable living in Kuwait and certain other countries and regions of the world. In such regions, where the summer months are extremely hot, systems with water cooled condensers are frequently relied upon for cooling residential and non-residential buildings. They are frequently relied upon because they consume less electricity and need-less power during peak hours. For example, studies have shown that systems with water cooled condensers consumed 25% less electricity and needed 40% less power at peak loads than other air conditioning systems.
In a system with a water cooled condenser as described herein, the cooling tower is a key piece of equipment. Commonly used counterflow water cooling towers comprise an upright casing which supports an elevated water distribution system, an underlying fill and means such as a powered fan or fans for drawing ambient-derived air currents into and through the tower casing and fill. They also include a water collection basin for collecting the cooled water. The distribution system serves to receive initially hot water from the condenser of an air conditioning system and distribute the same by gravitation through the underlying fill structure. The latter can be of the splash or film variety, but in all cases serves to effect a thermal interchange relationship between the initially hot water descending through the fill and the counter currently upwardly flowing air currents. In such towers, thermal energy is transferred to the ambient air through a humidification process.
Cooling towers use a large flow of air in providing cooler water temperatures to thereby improve the performance of the air conditioning systems. However, this improved performance significantly increases the costs for the increase in fan power and water consumption. This latter is of special concern in Kuwait and other countries where the soft water is produced through sea water desalination. In the prior art cooling towers, the temperature of the water leaving the cooling tower is the controlling parameter and the reduction of the leaving water temperature is controlled by the air flow through the tower. This approach has been universally practiced.
In the present invention, the dry bulb temperature of the air leaving the cooling tower is used as an additional parameter along with the temperature of the water leaving the cooling tower which is fixed by the designer of the air conditioning system. For example, using the dry bulb temperature of the leaving air to control air flow to allow only minimum moisture evaporation to meet the cooling demand can be used to reduce the electricity and water consumption. This can be achieved by keeping the dry bulb temperature of the air leaving the cooling tower close to the entering water temperature in the cooling tower.
In essence, the present invention contemplates a cooling tower for use in air conditioning system for cooling residential and non-residential buildings in areas of high temperature and particularly in areas of extreme heat. The cooling tower comprises a generally horizontal water collection basin and an upright casing above the collection basin. The tower also includes an air inlet in a lower portion thereof and an air outlet in an upper portion or top of the tower in a conventional manner. Means such as one or more fans are provided in an upper portion of the tower for inducing a flow of initially ambient air through the air inlet and up through and out of the tower. The cooling tower also includes a hot water distribution system for dispersing hot process water in an upper portion of the tower for gravitation through the flow of rising air so that the water is cooled by evaporation as it descends into the water collection basin. The cooling tower also includes means for sensing the temperature of the hot process water delivered to the hot water dispersing means and means for sensing the dry bulb temperature of the air leaving the cooling tower. Means are also provided for controlling the rotational speed to the fan or fans to maintain the dry bulb temperature of the air leaving the tower to approximately the temperature of the hot process water delivered to the hot process water dispersing means. In effect, the means for controlling the fan or fans will minimize the difference between the dry bulb temperature of the air leaving the tower and the temperature of the hot process water delivered to the hot water dispersing means.
In a preferred embodiment of the invention, the control will reduce the difference between the hot process water (T1) and the dry bulb temperature of the air leaving the tower (Tdbt2) to approach 0. This temperature difference represents a master control for regulating the air flow through the cooling tower by a variable frequency drive. The maintenance of the leaving water temperature to a predetermined value is then achieved by a sub-master control which will not allow the fan speed to be reduced further in case the temperature of the cooled water (T2) reaches the predetermined value.
The invention will now be described in connection with the accompanying drawings wherein like reference numerals have been used to designate like parts.